package cn.touna.jss.modules.third.baihang.sdk.util;


/**
 * 功能描述：提供base64字符串与字节数组的编解码转换
 */
public class Base64{
    /**
     * Translates the specified byte array into a Base64 string as per
     * Preferences.put(byte[]).
     */
    public static String byteArrayToBase64(byte[] a){
        return byteArrayToBase64(a, false);
       
    }

    /**
     * Translates the specified byte array into an "aternate representation"
     * Base64 string. This non-standard variant uses an alphabet that does not
     * contain the uppercase alphabetic characters, which makes it suitable for
     * use in situations where case-folding occurs.
     */
    public static String byteArrayToAltBase64(byte[] a){
        return byteArrayToBase64(a, true);
    }

    private static String byteArrayToBase64(byte[] a, boolean alternate){
        int aLen = a.length;
        int numFullGroups = aLen / 3;
        int numBytesInPartialGroup = aLen - 3 * numFullGroups;
        int resultLen = 4 * ((aLen + 2) / 3);
        StringBuffer result = new StringBuffer(resultLen);
        char[] intToAlpha = (alternate ? intToAltBase64 : intToBase64);

        // Translate all full groups from byte array elements to Base64
        int inCursor = 0;
        for(int i = 0; i < numFullGroups; i++){
            int byte0 = a[inCursor++] & 0xff;
            int byte1 = a[inCursor++] & 0xff;
            int byte2 = a[inCursor++] & 0xff;
            result.append(intToAlpha[byte0 >> 2]);
            result.append(intToAlpha[(byte0 << 4) & 0x3f | (byte1 >> 4)]);
            result.append(intToAlpha[(byte1 << 2) & 0x3f | (byte2 >> 6)]);
            result.append(intToAlpha[byte2 & 0x3f]);
        }

        // Translate partial group if present
        if(numBytesInPartialGroup != 0){
            int byte0 = a[inCursor++] & 0xff;
            result.append(intToAlpha[byte0 >> 2]);
            if(numBytesInPartialGroup == 1){
                result.append(intToAlpha[(byte0 << 4) & 0x3f]);
                result.append("==");
            }else{
                // assert numBytesInPartialGroup == 2;
                int byte1 = a[inCursor++] & 0xff;
                result.append(intToAlpha[(byte0 << 4) & 0x3f | (byte1 >> 4)]);
                result.append(intToAlpha[(byte1 << 2) & 0x3f]);
                result.append('=');
            }
        }
        // assert inCursor == a.length;
        // assert result.length() == resultLen;
        return result.toString();
    }

    /**
     * This array is a lookup table that translates 6-bit positive integer index
     * values into their "Base64 Alphabet" equivalents as specified in Table 1
     * of RFC 2045.
     */
    private static final char intToBase64[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
            'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e',
            'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
            'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'};

    /**
     * This array is a lookup table that translates 6-bit positive integer index
     * values into their "Alternate Base64 Alphabet" equivalents. This is NOT
     * the real Base64 Alphabet as per in Table 1 of RFC 2045. This alternate
     * alphabet does not use the capital letters. It is designed for use in
     * environments where "case folding" occurs.
     */
    private static final char intToAltBase64[] = {'!', '"', '#', '$', '%', '&', '\'', '(', ')', ',', '-',
            '.', ':', ';', '<', '>', '@', '[', ']', '^', '`', '_', '{', '|', '}', '~', 'a', 'b', 'c', 'd',
            'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w',
            'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '?'};

    /**
     * Translates the specified Base64 string (as per Preferences.get(byte[]))
     * into a byte array.
     * 
     * @throw IllegalArgumentException if <tt>s</tt> is not a valid Base64
     *        string.
     */
    public static byte[] base64ToByteArray(String s){
        return base64ToByteArray(s, false);
    }

    /**
     * Translates the specified "aternate representation" Base64 string into a
     * byte array.
     * 
     * @throw IllegalArgumentException or ArrayOutOfBoundsException if
     *        <tt>s</tt> is not a valid alternate representation Base64 string.
     */
    public static byte[] altBase64ToByteArray(String s){
        return base64ToByteArray(s, true);
    }

    private static byte[] base64ToByteArray(String s, boolean alternate){
        byte[] alphaToInt = (alternate ? altBase64ToInt : base64ToInt);
        int sLen = s.length();
        int numGroups = sLen / 4;
        if(4 * numGroups != sLen)
            throw new IllegalArgumentException("String length must be a multiple of four.");
        int missingBytesInLastGroup = 0;
        int numFullGroups = numGroups;
        if(sLen != 0){
            if(s.charAt(sLen - 1) == '='){
                missingBytesInLastGroup++;
                numFullGroups--;
            }
            if(s.charAt(sLen - 2) == '=')
                missingBytesInLastGroup++;
        }
        byte[] result = new byte[3 * numGroups - missingBytesInLastGroup];
        char[] a = s.toCharArray();
        // Translate all full groups from base64 to byte array elements
        int inCursor = 0, outCursor = 0;
        for(int i = 0; i < numFullGroups; i++){
            int ch0 = base64toInt(a[inCursor++], alphaToInt);
            int ch1 = base64toInt(a[inCursor++], alphaToInt);
            int ch2 = base64toInt(a[inCursor++], alphaToInt);
            int ch3 = base64toInt(a[inCursor++], alphaToInt);
            result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
            result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
            result[outCursor++] = (byte) ((ch2 << 6) | ch3);
        }

        // Translate partial group, if present
        if(missingBytesInLastGroup != 0){
            int ch0 = base64toInt(a[inCursor++], alphaToInt);
            int ch1 = base64toInt(a[inCursor++], alphaToInt);
            result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));

            if(missingBytesInLastGroup == 1){
                int ch2 = base64toInt(a[inCursor++], alphaToInt);
                result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
            }
        }
        // assert inCursor == s.length()-missingBytesInLastGroup;
        // assert outCursor == result.length;
        return result;
    }

    /**
     * Translates the specified character, which is assumed to be in the
     * "Base 64 Alphabet" into its equivalent 6-bit positive integer.
     * 
     * @throw IllegalArgumentException or ArrayOutOfBoundsException if c is not
     *        in the Base64 Alphabet.
     */
    private static int base64toInt(char c, byte[] alphaToInt){
        int result = alphaToInt[c];
        if(result < 0)
            throw new IllegalArgumentException("Illegal character " + c);
        return result;
    }

    /**
     * This array is a lookup table that translates unicode characters drawn
     * from the "Base64 Alphabet" (as specified in Table 1 of RFC 2045) into
     * their 6-bit positive integer equivalents. Characters that are not in the
     * Base64 alphabet but fall within the bounds of the array are translated to
     * -1.
     */
    private static final byte base64ToInt[] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1,
            -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
            25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
            43, 44, 45, 46, 47, 48, 49, 50, 51};

    /**
     * This array is the analogue of base64ToInt, but for the nonstandard
     * variant that avoids the use of uppercase alphabetic characters.
     */
    private static final byte altBase64ToInt[] = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7,
            8, -1, 62, 9, 10, 11, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 12, 13, 14, -1, 15, 63, 16, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, 17, -1, 18, 19, 21, 20, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
            43, 44, 45, 46, 47, 48, 49, 50, 51, 22, 23, 24, 25};
}
